The driver was taken to hospital with burns as emergency services worked to extinguish the fire.

Video footage on social media showed a large plume of smoke seen across the Swedish capital.

An emergency services spokesperson quoted in Sweden's Aftonbladet news outlet said the bus, which was powered by natural gas, was believed to have attemped to enter into a tunnel with height warnings, before hitting the barriers and exploding the gas tank on the roof.

Police said the incident was being treated as a "traffic accident" and was not believed to be terrorism-related.